$1.(8$ points$)$ We talked about the Feistel cipher in class. Why did we at least for now restrict ourselves to discussion of

the feistel cipher, rather than an arbitrary reversible substitution block cipher like in Table $4\mathrm{.}1$ of our notes?

$2.$ a$)[4$ points$]$ Describe to me the difference between diffusion and confusion in regards to the design goals of a cipher.

b$)[6$ points$]$ Given the DES cipher, explain the parts of the algorithm that give diffusion and the parts of the algorithm

that do confusion. While I know there is some crossover here, give a rationale for what parts more heavily focus on

diffusion or confusion or why some function might have both.

$3.(10$ points$)$ a$)$ What is the avalanche effect? Using a DES calculator found online, show an example of this. Give me

enough data in this answer so I can replicate your result, so give me any keys, data or results that you get. Of course also

tell me the calculator you used, as well as any initialization vector set.

$4.$ a$)[10$ points$]$ Encrypt the hexadecimal string C$5$ with a feistel cipher. Your function F should simply convert the

bitstring it is given to all $1$s$.$ Do this for two rounds.

b$)[5$ points$]$ How secure is this cipher? Do you notice any pattern in what is being produced given the input?